Thermoelectric Properties Of Benzothiadiazole Dithienyl Platinum Acetylide Polymers And Their Composites

As a green energy material,thermoelectric materials can directly convert heat energy and electric energy through carier movement in solids.Organic thermoelectric materials have the characteristics of small size,light weight,no noise and no pollution,and do not need conversion medium and mechanical movable parts.They are considered to have considerable application prospects in sustainable green energy.However,there are still problems such as unclear structure-effect relationship between structure and Seebeck coefficient and low thermoelectric performance.In this paper,the benzothiadiazole dithienyl platinum acetylide polymers was studied and doped with trifluoromethanesulfonic acid?TFA?to obtain good thermoelectric properties.The TFA doping mechanism was studied and the carrier type was determined.Then,by additionally adding FeCl₃ in the TFA,the thermoelectric performance was further improved and the reason for the improvement of the thermoelectric performance was explained.The P?TBT-Pt?with better thermoelectric performance and the PTBT without platinum acetylide structure were combined with single-walled carbon nanotubes?SWCNT?to study the effect of platinum acetylide structure on the thermoelectric properties of polymer/SWCNT composites.It has been found that embedding a platinum acetylide structure in a conjugated backbone is beneficial to the improvement of thermoelectric properties.The details are as follows:1.According to the Density Functional Theory?DFT?calculations,it is found that the introduction of platinum into the conjugated polymer structure can effectively adjust the electronic density distribution and increase the Seebeck coefficient.Thus,two metal platinumacetylenicpolymersP?TBT-Pt?andP?TBTC6-Pt?containing benzothiadiazole dithiophene units in the main chain structure were designed and synthesized.Doping with trifluoromethanesulfonic acid?TFA?,the maximum Seebeck coefficient of P?TBT-Pt?is-2.9±0.24 mV K^-1,the maximum Power factor is 43.73±9.95?W m^-1 K^-2;the maximum Seebeck coefficient of P?TBTC6-Pt?is-1.94±0.16mV K^-1,the maximum Power factor is 6.66±1.24?W m^-1 K^-2.Through research,it is proved that the doping mechanism is n-type self-doping,forming N⁺-H covalent bond,and the carrier type is dominated by CF₃SO₃^-ion.2.Based on the results in Chapter 3,it is preferred that P?TBT-Pt?is double doped with TFA(7 mol L^-1)and FeCl₃.The addition of FeCl₃ increases the contact area of the TFA solution with the surface of the P?TBT-Pt?film,and the synergistic effect increases the doping efficiency of TFA.At the same concentration,more n-type self-doping occurred,the concentration of CF₃SO₃^-ions increased,the conductivity was improved,and FeCl₃ formed crystals on the surface of P?TBT-Pt?film,which played the role of energy filtration and improved the Seebeck coefficient.The maximum conductivity is20.98 S m^-1,the maximum Seebeck coefficient is-2.49±0.17 mV K^-1,and the highest Power factor is 121.5±12.6?W m^-1 K^-2,which is 2.8 times that of TFA(7 mol L^-1)doping.3.Based on the results in Chapter 3 and 4,P?TBT-Pt?with better thermoelectric properties and PTBT with no platinum acetylide structure were combined with SWCNT to study the effect of platinum acetylide structure on the thermoelectric properties of polymer/SWCNT composites.It has been found that embedding a platinum acetylide structure in a conjugated backbone is beneficial to enhance the?-?interaction between the polymer and SWCNTs.P?TBT-Pt?is tightly attached to the SWCNT surface to form an interpenetrating network,thus slowing down the decrease of Seebeck coefficient and improving the thermoelectric performance.The highest PF value of P?TBT-Pt?/SWCNT composite at room temperature is almost three times that of PTBT/SWCNT composite.The highest PF value of P?TBT-Pt?/SWCNT composites under variable temperature is 158.6?W m^-1 K^-2.